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The main water pipe into our house is only a 1" ID pipe, but the city decided to install a 2" water meter for us, which has a significantly higher monthly service charge than a 1" meter (over $1000 more per year).

I found a couple of websites (like this one) that calculate the required water-meter-size based on the number of showers, toilets, sinks, and such in the house. They all place us solidly into the 1" size range. But we live on a hill and the incoming water pressure into our house is only 35psi. So I'm trying to understand the following things:

  • Do I need to correct the required water meter size for the lower pressure? If so, by how much?
  • If the main pipe to the house is only 1" ID, would a water meter bigger than 1" even help at all?
  • Is a 1" water meter equivalent in "size" (as far as flow impedance goes) to a 1" water pipe?

One of our neighbors with an identical floorplan said he got the city to swap his meter out for a 1.5" at no charge and is not noticing any difference other than the $600 annual savings. I'm trying to figure out if it makes sense to be even more "aggressive" and have them down-size us to a 1" meter.

Note: This question is purely about things to consider when determining the right size of our water meter. I'm not looking for any off-topic policy advice on how to deal with the city.

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I take it you have a big house that requires a 1" pipe? In my experience, most residences need a 3/4" main. –  Edwin Feb 14 at 6:07
    
@Edwin 1" was pretty standard around my area, even for smaller houses. –  virtualxtc Feb 14 at 6:23
    
@Edwin We have about 3100 sq-ft. 3 full bathrooms, pool, sprinklers. We end up somewhere around 45 to 65 "fixture units" worth of water needed (depending on which site I use to calculate it, main difference are the sprinklers). 1" water meters seem to be the ones intended for anything between 38 and 89 fixture units. –  Markus A. Feb 14 at 16:35

2 Answers 2

up vote 1 down vote accepted

It's likely that the type of meter you have is called a PD meter.

PD Meters are very accurate, but do this at the expense of pressure.

My guess is that increasing the volume of the meter likely does do a little to reduce pressure drop. However, without the actual specs for each meter, it's impossible to say how much.

That said, **it is highly unlikely that a 2" meter in the middle of a 1" line it's making a $1000 (or even $400) per year difference in pressue. For less than $1000 you can can make a one time investment in a residential pressure booster.

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what do you mean that it is highly unlikely that it's making a $1000 per year difference? Where I live, in Philadelphia, the annual service charge difference between a 2" meter and a 1" meter is $690.48 (excluding storm-water fees). Doesn't seem unreasonable that the OP's district would be 50% more. Do you mean that the benefit of the larger meter doesn't equal $1000? –  Edwin Feb 14 at 6:04
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I like the idea of a pressure booster, could go down to a 3/4" with one. –  Edwin Feb 14 at 6:09
    
@Edwin I mean the reduction in (to borrow an EE term) 'resistance' in a 1" meter vs 2" meter (especially given it's in the middle of a 1" line) is not going to come anywhere close to providing $1000 worth of value. If he needed the full capacity of a 2" pipe and had one comeing in off the main, then it would be worth it. –  virtualxtc Feb 14 at 6:10
    
@Edwin,virtualxtc I love the idea of the pressure booster and considering to go down to even 3/4". That would save me another $200 a year! But this does raise some additional questions, that I decided to put in a separate question here: diy.stackexchange.com/questions/39027/… :) Thanks! –  Markus A. Feb 14 at 7:08

I (literally) dug up the information on our water meter: Currently we have a 2" Neptune T-10 installed. On their website they offer specifications for their different meters, including charts of pressure drop vs. flow-rate. I used some free software to quickly digitize the plots and stick them together onto one chart showing the pressure drop vs. flow rate for 4 different meter sizes:

enter image description here

So, if I assume (please correct me on these assumptions if they make no sense) that a 10% pressure drop would be noticeable (for us: 3.5psi), then I would hit this drop at 18gpm for a 3/4" meter and at 33gpm for a 1" meter. Given that the shower valve we installed provides 8gpm at 75psi (so probably less at 35psi), that means 2-3 people can take a shower at the same time with a 3/4" meter and more than 4 for a 1" meter.

So, I guess going with a 3/4" meter feels a little tight to me (unless we get a booster pump, of course), but a 1" meter should probably be just fine. I don't think we'd frequently be using more than 15gpm anyway, which would only imply a pressure drop of 1psi over the 2" meter.

Note: I'll leave @virtualxtc's answer as the selected one, since he pointed me in the right direction and summarizes things nicely.

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Do a test of how much water your shower uses. Shower heads reduce the flow a lot. In the US, federal law limits shower heads to 2.5 gpm at 80 psi since 1992. But, maybe you have older ones or modified them? –  Edwin Feb 14 at 19:11

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